It is generally known to mount a weft insertion gripper on the free end of a carrier in the form of a rigid rod or rapier, and to alternately drive the rapier into and out of the loom shed to carry out the weft insertion. For example, German Patent 1,535,491 (Kokkinis) discloses a loom in which the weft insertion is carried out by a gripper system including a rigid rapier rod having a U-shaped cross-section, with a toothed gear rack arranged thereon or therein, and including a drive gear that engages the toothed gear rack so as to alternately drive the rapier rod, and the gripper mounted thereon, into and out of the loom shed.
In order to achieve a precise lengthwise motion of the rapier rod and to prevent the rapier rod from lifting away from the drive gear, it is known to provide one or more guide rollers for supporting and guiding the rapier rod. Generally, such guide rollers are arranged in the area of the drive gear, above or on the opposite side of the rapier rod, so as to press the rapier rod against the drive gear and thus guide and support the rapier rod.
A disadvantage of the known roller bearing arrangements for the rapier rod is that substantial frictional forces are effective between the rollers and the rapier rod, which leads to a relatively high rate of wear on the rollers and the rapier rod. In this context, the roller bearings also cause thermal problems, since the friction between the rollers and the rapier rod generates a substantial amount of heat that must somehow be dissipated. Moreover, the rollers must be accelerated and then again decelerated together with the rapier rod for each movement of the rod into or out of the loom shed, so that the drive arrangement necessarily has a high rotational moment.
It is also known in the art to mount the weft insertion grippers on flexible tapes or bands which are connected to alternately rotating drive wheels for driving the grippers into and out of the loom shed. German Patent 3,916,591 (Esposito et al.), published European Patent Application 0,285,001 (Muller et al.), and U.S. Pat. No. 3,175,587 (Gove, Jr. et al.) each disclose gripper looms using such a system of weft insertion grippers mounted on flexible tapes or bands that are alternately rolled onto and off of drive wheels having a relatively large diameter. These three patent publications also disclose devices for pneumatically guiding the flexible bands.
The arrangement according to European Patent Application 0,285,001 provides a perforated gripper carrying band that engages teeth provided around the perimeter of a drive sprocket or drive wheel. Guidance for the flexible band is provided by one or more toothed guide rollers, and/or by a pneumatic guide element having two rows of pressurized air outlet holes on both sides of the row of drive teeth, as shown and described in connection with FIGS. 12, 13 and 15 of the reference. In the embodiment of FIG. 15, two pneumatic guide elements may be provided at different circumferential areas around the drive wheel, or the two air bearing bodies can be embodied in a one-piece manner so as to extend over the entire range in which the flexible band loops around the drive sprocket.
According to German Patent 3,916,591, the flexible gripper carrying band may either be perforated or non-perforated, and a pneumatic guide element is arranged particularly at the area above the band where the band is no longer in engagement with the drive wheel. The guide element includes a contact plate for guiding the upper surface of the flexible band, whereby holes extend vertically through the contact plate so as to introduce pressurized air into the space between the upper surface of the guide band and the guide plate. The guide element is rigidly mounted by flanges onto a lower guide arranged below the flexible band. The lower plate in turn is rigidly bolted to the machine frame of the loom.
U.S. Pat. No. 3,175,587 (Gove, Jr. et al.) discloses an arrangement of a plurality of arcuately curved hydrostatic air bearings around a portion of a circumference of a tape drive wheel, for guiding and holding the flexible weft insertion tape against the outer rim of the tape drive wheel, especially as the tape is unrolled from the wheel. Each air bearing comprises a single bearing body block having air apertures and air pockets formed therein. Such a construction fails to take into account that some contact wear between the tape and the bearing body is inevitable, and requires the entire bearing body to be replaced if the inner arcuate surface thereof becomes worn. Also, the distribution of air through the air pockets is not as uniform as could be desired. As a further disadvantage, the conventional interconnection of the several air bearings using flexible air lines with numerous T-fittings and joints is prone to leakage and failure.
In high speed looms using a flexible gripper carrying band it is absolutely necessary to provide a positive guidance for the flexible band directly after the point at which it leaves the drive wheel due to the centrifugal forces effective on the flexible band. Namely, centrifugal forces are effective on the flexible band as it is alternately rolled onto and off of the drive wheel, so that the flexible band would lift away from the drive wheel due to the arising forces if a positive guidance is not provided to hold the flexible band against the drive wheel. As discussed above, conventional arrangements of a flexible gripper carrying band use pneumatically operating guide means, as well as mechanical guide rollers, for supporting or guiding the flexible band.
On the other hand, in rapier looms using a substantially rigid rapier rod rather than a flexible band or tape for carrying the weft gripper, it is not necessary to provide such a positive guidance and support for counteracting centrifugal forces, because the rapier rod is not subjected to centrifugal forces since it is only subjected to a linear motion. For this reason, in the prior art it has been considered sufficient to carry out the guidance and support of rigid rapier rods by means of mechanical roller bearings or guide rollers as described above. However, such mechanical guide rollers suffer disadvantages of frictional wear and heating as also discussed above.